Present work suggests that mitochondrial Fo-F1, purified as described, has the highest reported Pi-ATP exchange activity. It is essentially free of adenylate kinase and phosphate transport protein. In highly resolving SDS-PAGE, it shows eighteen bands. The project is designed to purify it further to the minimum number of components and study the subunit arrangement and spatial relationship of various components. This would be achieved by using chemical as well as photo-affinity cross-linking reagents and the adducts will be identified with the help of site specific labels, subunit specific antibodies, and 2-dimensional SDS-PAGE, wherever applicable. It is hoped that the data would provide clues to the elucidation of mechanism of energy coupling processes that require intimate association of F1 and membrane components.